Many operators are beginning to commercialize evolved packet data gateway (ePDG). One of the advantages of ePDG is that it allows seamless handoff of communication services (voice, video, etc.) between long-term evolution (LTE) and wireless fidelity (WiFi).
But one of the drawbacks of ePDG technology may have longer connection establishment time comparing to other cellular technologies. Setting up APN connection on ePDG requires internet key exchange version 2 (IKEv2) Phase 1 tunnel setup, extensible authentication protocol method for universal mobile telecommunications system (UTMS) authentication and key agreement (EAP-AKA) authentication and child tunnel setup. With deteriorating cellular connection, this delay leads to bad user experience and access point name (APN) connection delay adds up when round-trip time (RTT) delay is high on WiFi connection.
Another disadvantage of LTE<->WiFi handoff is that APN connection is torn down completely on existing radio access technology (RAT) when connection is established on new RAT. The makes it more computation intensive especially for ePDG connection, which takes more time.